In a Layer-2 switch in an Internet Protocol (IP) network, performed is bandwidth management that controls output bandwidths of packets on a per-queue basis. Namely, a queue is set for each user terminal which is a destination, and a bandwidth of output packets in each queue is managed. Quality of Service (QOS: priority control, band control, etc.) for each user terminal is accomplished by the bandwidth management.
The QOS service guarantees a network user band to each user terminal under the contract (referred to as bandwidth guarantee). To guarantee the bandwidth, performed is a queue control based on, for example, token bucket. In bandwidth management for a plurality of queues, a token bucket is provided for each queue, packets are stored in a relevant queue, and when a token is left in the token bucket, outputting of a packet in the queue is permitted.
In a token bucket for each queue, bytes in number (bandwidth value) that can be outputted for a predetermined time period are accumulated according to a bandwidth (guaranteed bandwidth value) in which the communication is guaranteed under the contract or the like. This value is added at intervals of a predetermined time (referred to as cyclic update), whereas the number of outputted bytes are subtracted when outputting is requested (referred to as read update). As this, the guaranteed bandwidth is managed and controlled (on a per-queue basis).
After packets in each queue corresponding to the guaranteed bandwidth are outputted under the bandwidth management with the use of the token bucket, the token bucket is empty. However, when the bandwidth of the output line has a surplus even after a communication corresponding to the guaranteed bandwidth is made, a surplus bandwidth generates.
Namely, when the values of token buckets are zero or less, or no packets are stored in all queues before the token buckets are added and updated in the cyclic update, an empty time generates. A section of this empty time is called a surplus bandwidth because this empty time generates after the set bandwidth is satisfied.
When there still remains a queue in which a packet(s) is stored in such occasion, a communication can be made by using the surplus bandwidth. Namely, the surplus bandwidth can be distributed to the users to provide further service to the users.
In order to improve the quality of the communication service to the users, the bandwidth management with higher accuracy is demanded even at the time of a communication using a surplus bandwidth while considering demands from the users of accommodated user terminals.
[Patent Document] Japanese Patent Application Laid-Open Publication No. 2005-268846
[Patent Document] Japanese Patent Application Laid-Open Publication No. 2005-184709
[Patent Document] Japanese Patent Application Laid-Open Publication No. 2007-181085